Double-wall inflatable column assembly for a dock leveler

ABSTRACT

A dock leveler for a truck loading dock includes a pivotal deck that is actuated by an inflatable column assembly. The inflatable column assembly includes an outer pliable tube that contains a more airtight inflatable bladder. The pliable tube is made of a tough fabric to protect the inner bladder. In some embodiments, the pliable tube has a generally vertical cylindrical shape that can provide a heavy deck with ample columnar support.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention The subject invention generally relates to dock levelers, and more specifically to a dock leveler whose deck is raised by an inflatable member.

[0002] 2. Description of Related Art

[0003] Loading docks often include a dock leveler to facilitate the loading or unloading of a truck's cargo. The dock leveler provides a bridge that material handling equipment and personnel can use to travel between a loading dock platform and the bed of the truck. Dock levelers usually include a deck or ramp that can pivot about its rear edge to raise or lower its front edge. Often a lip plate extends from the front edge of the deck and is adapted to engage the rear of the truck bed. The lip plate is usually movable between a stored, retracted position and an extended, vehicle-engaging position. The pivotal movement of the deck enables the dock leveler to set the lip plate on or remove it from the truck bed.

[0004] To pivot a deck, a dock leveler usually includes some type of actuator that extends, expands or otherwise moves to force the deck upward. Downward movement of the deck may be achieved by relying on weight of deck or by physically pushing the deck back down by way of an external force or weight, such as the weight of a person standing on the deck.

[0005] There are currently a variety of well-known actuators available. Some common ones include, hydraulic cylinders, pneumatic cylinders, coil springs, high-pressure air springs, linear motors, and inflatable actuators. Inflatable actuators are perhaps one of the more recent types of actuator. Examples of inflatable actuators can be found in U.S. Pat. Nos. 5,475,888; 5,522,108; 5,802,651; 5,996,156 and 6,267,448. In these examples, a low-pressure blower inflates a bag disposed underneath the deck of a dock leveler or underneath the bed of a truck. As the bag inflates, it lifts the deck or truck bed.

[0006] Although inflatable actuators can be effective, the choice of material for the bag is critically important. The material needs strength to support the weight of the deck, pliability at low temperatures, durability to withstand repeated cycling, and the material should be able to hold air pressure. There are limited materials that can satisfy all these needs. For instance, some of the stronger materials may have insufficient pliability; thinner materials may be more pliable, but not as durable; some fabrics are quite strong, but are too porous to hold air pressure; and other materials are too expensive. Consequently, it can be difficult to find a single material that provides all the properties necessary for an effective inflatable actuator.

SUMMARY OF THE INVENTION

[0007] In some embodiments, the deck of a dock leveler is lifted by an inflatable column assembly that comprises an outer pliable tube and an inner bladder.

[0008] In some embodiments, the outer pliable tube is stronger than the bladder.

[0009] In some embodiments, the bladder is more airtight than the outer pliable tube.

[0010] In some embodiments, the bladder is inflatable and used primarily for expanding the outer tube.

[0011] In some embodiments, the outer pliable tube serves as a backup for the bladder.

[0012] In some embodiments, the bladder, when inflated and unrestrained by the outer pliable tube, has a non-cylindrical shape that is substantially larger than the outer tube.

[0013] In some embodiments, the bladder comprises two pliable sheets that are fused together.

[0014] In some embodiments, the inflatable column assembly is inflated through a nozzle having a diverging airflow passageway.

[0015] In some embodiments, the nozzle includes an air passageway that curves smoothly between an obtuse angle.

[0016] In some embodiments, the blower that inflates the bladder is pivotally attached to a hinge of the dock leveler's deck, thereby providing a flexible point of attachment.

[0017] In some embodiments, the blower is mounted at a substantially fixed location.

[0018] In some embodiments, the blower is attached to a mounting plate that protects the blower from impact during shipment and installation.

[0019] In some embodiments, the dock leveler includes a lip that extends linearly relative to the deck.

[0020] In some embodiments, the dock leveler includes a lip that pivots relative to the deck.

[0021] In some embodiments, the dock leveler includes a lip that pivots and slides relative to the deck.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a side view of a dock leveler whose deck, shown in a cross-traffic position, is actuated by an inflatable column assembly.

[0023]FIG. 2 is similar to FIG. 1, but with the inflatable column assembly inflated to lift the deck.

[0024]FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 7.

[0025]FIG. 4 is similar to FIG. 1, but with the deck of the dock leveler resting upon the rear of a truck bed.

[0026]FIG. 5 is a top view of bladder of the inflatable column assembly.

[0027]FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 5.

[0028]FIG. 7 is a front view of the dock leveler in its raised position of FIG. 2.

[0029]FIG. 8 is a cross-sectional view taken along line 8-8 of FIG. 3.

[0030]FIG. 9 is similar to FIG. 1, but showing a dock leveler with a sliding lip extension.

[0031]FIG. 10 is similar to FIG. 9, but with the inflatable column assembly inflated to lift the deck of the dock leveler.

[0032]FIG. 11 is similar to FIG. 9, but with the deck of the dock leveler resting upon the rear of a truck bed.

[0033]FIG. 12 is similar to FIG. 1, but showing a dock leveler with another type of lip extension.

[0034]FIG. 13 is similar to FIG. 12, but with the inflatable column assembly inflated to lift the deck of the dock leveler.

[0035]FIG. 14 is similar to FIG. 12, but with the deck of the dock leveler resting upon the rear of a truck bed.

[0036]FIG. 15 is a cross-sectional view taken along line 15-15 of FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0037]FIGS. 1-4 show various operating positions of a dock leveler 10, which is installed at a loading dock 12 so a vehicle 14 (e.g., truck, trailer, etc.) can be readily loaded or unloaded of its cargo. Dock leveler 10 includes a pivotal deck 16 with an lip extension 18 that together provide a path for personnel and material handling equipment to travel between a platform 20 of the dock and vehicle 14. A hinge 22 adjacent a back edge 24 of deck 16 allows an inflatable column assembly 26 to pivot deck 16, thereby raising or lowering a front edge 28 of the deck, which enables the dock leveler to set lip extension 18 on or remove it from the truck bed. Lip 18 extends from deck 16 to bridge the gap between front edge 28 and a rear edge 30 of vehicle 14.

[0038] The sequence of operation at dock 12 typically begins with dock leveler 10 at its stored, cross-traffic position, as shown in FIG. 1. In this position, inflatable column assembly 26 is deflated, lip 18 is at its pendant position supported by a set of lip keepers 32, and the top surface of deck 16 is generally flush with platform 20. Arrow 34 represents vehicle 14 backing the rear edge of it truck bed toward a bumper 36 of dock 12.

[0039] Next, in FIGS. 2 and 3, a source of pressurized air, such as a blower 38 is energized to inflate column assembly 26. The source of pressurized air preferably delivers low-pressure air (i.e., less than 10 psig). A centrifugal blower is one example of a source of low-pressure air. As inflatable column assembly 26 expands, it forces deck 16 upward. Lip 18, which a hinge 40 pivotally connects to front edge 28 of deck 16, pivots outward to extend out over the truck bed of vehicle 14. Arrow 42 of FIG. 2 schematically represents any actuator able to move lip 18 (e.g., by acting upon a lug 19 fixed to lip 18). Examples of such a lip actuator include, but are not limited to, hydraulic cylinders, pneumatic cylinders, low-pressure air actuator, coil springs, high-pressure air springs, linear motors, mechanical linkages responsive to the movement of deck 16, and various combinations thereof.

[0040] After lip 18 is extended out over rear edge 30 of vehicle 14, blower 38 is de-energized to deflate column assembly 26. This allows deck 16 to descend and lip 18 to rest upon the truck bed of vehicle 14, as shown in FIG. 4. In this position, cargo can be readily added or removed from vehicle 14.

[0041] To enable inflatable column assembly 26 to raise and lower deck 16, the column assembly includes a pliable outer tube 44 containing an inner bladder 46, as shown in FIG. 3. A tubular member 48 and a nozzle 50 connect a discharge outlet 52 of blower 38 to the interior of bladder 46, so air discharged from blower 38 inflates bladder 46. As bladder 46 inflates, it forces outer tube 44 to expand, which pushes deck 16 upward. As bladder 46 inflates, it also forces air out from within an air gap 45 between outer tube 44 and bladder 46. Air gap 45 becomes smaller as the air escapes through various openings, such as an opening 90 for nozzle 50, and various seams or other minute openings in outer tube 44. To lower deck 16 back down, blower 38 is de-energized, which allows the deck's weight to push the air back out of bladder 46. The air escapes to atmosphere by exhausting in series flow back through nozzle 50, tubular member 48 and blower 38 (causing the blower to back spin). The resulting flow resistance provides deck 16 with a controlled descent. In some embodiments, a bracket 54 couples blower 38 to a hinge pin 56 of hinge 22 so that the movement of blower 38 tracks the pivotal movement of deck 16 of dock leveler 10. According to this tracking feature, blower 38 will pivot about hinge pin 56 as the deck pivots about that same hinge pin. Typically, however, slack in the connection between blower 38 and inflatable column assembly 26 a (such connection to be described in greater detail below) will result in the blower pivoting at a slower rate than deck 16, and thus pivoting through less of an arc for a given arc of deck movement. The benefit of the pivotal mounting of blower 38 in this manner is that it reduces strain in the tubing or conduits connecting the blower to the inflatable column assembly 26 a, given that relative movement between deck 16 and blower 38 is minimized by pivotally mounting the blower.

[0042] Referring to FIGS. 5 and 6, bladder 46 can be made relatively airtight by making the bladder of two pliable sheets 46 a and 46 b that consist of an air-impermeable material, such as a pliable plastic having a polyester, polyurethane, polyethylene, or polypropylene base. In some embodiments, bladder 46 can be made an eight-mil thick aromatic ether based urethane, such as a Deerfield Duraflex Polyether PT9400S. Making bladder 46 of just two sheets 46 a and 46 b minimizes the number of required seams. Alternate bladder embodiments are shown in FIGS. 7 and 8. In FIG. 7, a bladder 46′ comprises a pliable sheet 46 a′ that is folder over onto itself such that a crease 47 exists along a first portion of the bladder's peripheral edge. The remainder of the bladder's peripheral edge is sealed to create a sealed joint 58′. In FIG. 8, a bladder 46″ comprises a tubular sheet 46 a″ having two sealed joints 58″ at opposite ends thereof. Any seams of the bladder, such as peripheral seam 58, are preferably created by fusing sheets 46 a and 46 b together, whereby seam 58 and sheets 46 a and 46 b are of the same material.

[0043] The unrestrained inflated shapes of bladders 46, 46′ and 46″ are not necessarily cylindrical nor complemental to the expanded shape of outer tube 44. A bladder can assume other shapes including, but not limited to, rectangular, conical, trapezoidal, pyramid-shaped, or pillow-shaped (as shown). When bladder 46 is inflated and unrestrained (e.g., bladder 46 removed from within the confines of outer tube 44), its unrestrained maximum air capacity (maximum volume of air bladder 46 can hold) is greater than the maximum air capacity of outer tube 44 when unrestrained (e.g., tube 44 removed from underneath deck 16). Air can enter or exit bladder 46 through a hole 60 in sheet 46 a. Nozzle 50 includes a flange 62 that is fused, bonded or otherwise attached to sheet 46 a around hole 60. Flange 62 may be inside or outside of bladder 46.

[0044] To promote airflow, nozzle 50 includes a smoothly curved and diverging air passageway 64. A centerline 66 of air passageway 64 preferably curves so an air entry path 68 and an air exit path 70 define an obtuse angle 72, as opposed to a sharp right angle. The air passageway 64 diverging from an inlet 74 to an outlet 76 improves the flow of air into bladder 46, thereby increasing the speed at which deck 16 can be lifted for any given capacity blower.

[0045] To improve the burst strength, durability, appearance, and columnar support strength of inflatable column assembly 26, outer tube 44 is made of a tough nylon material that provides a generally vertical cylinder when expanded from within by bladder 46. In some embodiments, outer tube 44 is made of a nylon ballistic cloth that conforms to MIL-C-12369F(GL). To protect the nylon from ultraviolet radiation, the exterior of tube 44 has a urethane coating of no more than 0.75 ounces per square yard.

[0046] Referring to FIG. 7, outer tube 44 is attached to an upper pliable sheet 80 along an upper perimetric seam 82 (e.g., sewn joint), and is attached to a lower pliable sheet 84 along a lower perimetric seam 86. In cases where outer tube 44 is cylindrical and vertical, lower perimetric seam 86 may be generally circular, and upper perimetric seam 82 may be generally elliptical. In cases where outer tube 44 is cylindrical but set at an angle (e.g., embodiment of FIG. 10), both the lower and upper perimetric seams may be elliptical. Or, when an expanded outer tube is generally perpendicular to the deck, the upper perimetric seam may be circular and the lower seam may be elliptical. Slicing a cylinder creates the elliptical shape. To minimize potential areas of leakage, a longitudinal seam 88 of outer tube 44 is positioned where its length is minimized, i.e., positioned away from front edge 28 of deck 16.

[0047] Outer tube 44 can also serve as an inflated backup for bladder 46, whereby inflatable column assembly 26 does not have to rely on bladder 46 alone for support. For instance, if bladder 46 were to lose its effectiveness due to a seam or material failure during maximum inflation, the released air would become trapped inside the expanded outer tube 44 causing deck 16 to descend slowly as the air slowly leaked through various openings, such as an opening 90 for nozzle 50, seams 82, 86 or 88, and other minute openings in outer tube 44.

[0048] Upper sheet 80 of outer tube 44 is held in tension across several support beams 92 of deck 16, thereby providing inflatable column assembly 26 with a broad surface against which outer tube 44 may push up against deck 16. If sheet 80 were not held in tension, its pliability may allow the inflated column assembly 26 to squeeze between the deck's spaced support beams 92. In some cases, upper sheet 80 is made of the same pliable sheet material as outer tube 44. This not only minimizes the weight load on inflatable column assembly 26 but also provides column assembly 26 with an overall thinner profile when deflated.

[0049] Referring to FIG. 8, outer tube 44 can be joined to upper sheet 80 by first slitting the perimeter of outer tube 44 at numerous points to increase the flexibility of outer tube 44 around its perimeter. The slits create a series of peripheral tabs 89 that can be easily folded outward to create a flange 93. Flange 93 of outer tube 44 can then be readily sewn to upper sheet 80 along a seam 82. In cases where the material of outer tube 44 is sufficiently pliable, flange 93 can be sewn to sheets 80 and 84 without having to slit the flange.

[0050] Upper sheet 80 can be held in tension in a variety of ways. For example, steel support bars 94 could be held within hems 96 sewn along either side of upper sheet 80. Anchors 98 can then connect bars 94 to support beams 92 or another part of deck 16. Anchors 98 are schematically illustrated to represent any connector that can hold upper sheet 80 taut across the underside of deck 16. Examples of anchor 98 include, but are not limited to, an eyebolt, turnbuckle, wire, strap, hook, chain, etc.

[0051] Lower sheet 84 of inflatable column assembly 26 can also be made of the same pliable sheet material as outer tube 44. Outer tube 44 can be attached to lower sheet 84 in the same manner that tube 44 is attached to upper sheet 80. Lower sheet 84 is preferably attached to a plastic pallet 100 that rests atop a bottom surface 102 of dock leveler 10 or rests at the bottom of a pit within which a dock leveler is installed. By not having pallet 100 fixed or attached to surface 102, pallet 100 and inflatable column assembly 26 are free to settle to their naturally central position, where outer tube 44 assumes a generally vertical orientation. In addition, pallet 100 can be readily lifted manually for periodic cleaning of bottom surface 102.

[0052] In another embodiment, shown in FIGS. 9-11, an inflatable column assembly 26′ operates a dock leveler 104 whose deck 106 includes a lip extension 108 that moves linearly relative to the deck. The function of inflatable column assembly 26′ is generally the same inflatable column assembly 26, with FIGS. 9, 10 and 11 corresponding to FIGS. 1, 2 and 4, respectively. However, inflatable column assembly 26′ is disposed at an angle from the vertical when expanded, as shown in FIG. 10. Inflatable column assembly 26′ in such a non-vertical orientation may be preferred in some applications. Arrow 110 of FIG. 10 is similar to arrow 42 of FIG. 2 in that both arrows schematically represent any actuator able to move lip 18 or 108. As mentioned earlier, examples of such a lip actuator include, but are not limited to, hydraulic cylinders, pneumatic cylinders, low-pressure air actuator, coil springs, high-pressure air springs, linear motors, mechanical linkages responsive to the movement of the deck, and various combinations thereof.

[0053] In another embodiment, shown in FIGS. 12-14, an inflatable column assembly 26″ operates a dock leveler 120 whose deck 122 includes a lip extension 124 that pivots and slides relative to the deck. Details of lip extension 124 can be found in U.S. Pat. No. 4,920,598, which is specifically incorporated by reference herein. In this embodiment, the structure and function of inflatable column assembly 26″ is generally the same as inflatable column assembly 26, wherein FIGS. 12, 13 and 14 correspond to FIGS. 1, 2 and 4, respectively. Arrow 121 of FIG. 13 is similar to arrow 42 of FIG. 2 in that both arrows schematically represent any actuator able to move lip 18 or 124. Examples of such a lip actuator include, but are not limited to, hydraulic cylinders, pneumatic cylinders, low-pressure air actuator, coil springs, high-pressure air springs, linear motors, mechanical linkages responsive to the movement of the deck, and various combinations thereof.

[0054] Inflatable column assembly 26″ includes some unique features pertaining to its source of pressurized air. In particular, the source of pressurized air, e.g., a blower 38′, is mounted at a substantially fixed location relative loading dock 12 and nozzle 50 is substantially fixed relative to deck 122. To mount blower 38′, a steel plate 128 is welded or otherwise attached to a frame member 130 of dock leveler 120. Lugs 132 extending from blower 38′ are fastened to tabs 134 and 136, which extend from plate 128. Plate 128 not only holds a housing 138 of blower 38′ substantially stationary, but plate 128 also helps protect blower 38′ from impact during installation or shipping of dock leveler 120. A strap clamp 140 (see detail in FIG. 17) attaches nozzle 50 to a bracket 101 mounted to the underside of the deck as shown in FIG. 17. Bracket 101 may also be attached to other structure associated with deck 122. Strap clamp 140 extends around nozzle 50, and a fastener 141 attaches strap clamp 140 to bracket 101.

[0055] To accommodate the pivotal movement of deck 122, a flexible tubular member 142 (e.g., a hose) couples an outlet 52′ of blower 38′ to inlet 74 of nozzle 50. As deck 122 pivots to its positions of FIGS. 12-14, the flexibility of tubular member 142 maintains outlet 52′ in fluid communication with inlet 74. Otherwise, the functions of inflatable column assembly 26″, blower 38′, tubular member 142, and nozzle 50 (of dock leveler 120) are same as inflatable column assembly 26, blower 38, tubular member 48 and nozzle 50 (of dock leveler 10), respectively.

[0056] Although the invention is described with respect to a preferred embodiment, modifications thereto will be apparent to those skilled in the art. Therefore, the scope of the invention is to be determined by reference to the claims that follow. 

We claim:
 1. A dock leveler for a vehicle at a loading dock, comprising: a deck having a rear edge and a forward edge, wherein the rear edge is adapted to be pivotally coupled to the loading dock to enable vertical movement of the forward edge relative to the loading dock; a lip extension adjacent the forward edge of the deck and being moveable relative thereto, the lip extension being adapted to engage the vehicle; a pliable tube disposed underneath the deck; a bladder disposed inside the pliable tube and defining an air gap therebetween, the bladder being inflated when the deck is raised, and deflated when the deck is lowered; and a source of pressurized air coupled to the bladder such that air discharged from the source of pressurized air pressurizes air inside the bladder to create greater air pressure inside the bladder than inside the air gap, whereby the source of pressurized air inflates the bladder, which in turn expands the pliable tube to push the deck upward.
 2. The dock leveler of claim 1, wherein the pliable tube has a first unrestrained maximum air capacity, and the bladder has a second unrestrained maximum air capacity that is greater than the first maximum unrestrained air capacity of the pliable tube.
 3. The dock leveler of claim 1, wherein the air gap gets smaller upon inflating the bladder.
 4. The dock leveler of claim 1, wherein the pliable tube is substantially cylindrical when expanded.
 5. The dock leveler of claim 1, wherein the bladder deviates from a cylindrical shape when inflated and unrestrained.
 6. The dock leveler of claim 1, wherein the bladder is generally pillow-shaped when inflated and unrestrained.
 7. The dock leveler of claim 1, wherein the bladder is more airtight than the pliable tube.
 8. The dock leveler of claim 1, wherein the pliable tube is stronger than the bladder.
 9. The dock leveler of claim 1, wherein the bladder comprises two pliable sheets integrally joined to each other by a peripheral joint, whereby the two pliable sheets and the peripheral joint are of the same material.
 10. The dock leveler of claim 1, wherein the bladder comprises a tubular sheet having two sealed joints at opposite ends thereof.
 11. The dock leveler of claim 1, wherein the bladder comprises a pliable sheet having a peripheral edge, wherein a crease exists along a first portion of the peripheral edge and a sealed joint exists along a second portion of the peripheral edge.
 12. The dock leveler of claim 1, further comprising a nozzle that couples the source of pressurized air to the bladder, wherein the nozzle defines an air passageway that provides a diverging flow pattern of air discharged from the source of pressurized air.
 13. The dock leveler of claim 12, wherein the air passageway extends along a curved centerline that defines an obtuse angle.
 14. The dock leveler of claim 1, wherein the lip extension is linearly moveable relative to the deck.
 15. The dock leveler of claim 1, wherein the source of pressurized air remains at a substantially fixed location.
 16. The dock leveler of claim 1, further comprising a flexible tube that couples the source of pressurized air to the bladder.
 17. A dock leveler for a vehicle at a loading dock, comprising: a deck having a rear edge and a forward edge, wherein the rear edge is adapted to be pivotally coupled to the loading dock to enable vertical movement of the forward edge relative to the loading dock; a lip extension adjacent the forward edge of the deck and being moveable relative thereto, the lip extension being adapted to engage the vehicle; a pliable tube disposed underneath the deck, wherein the pliable tube has a first unrestrained maximum air capacity; a bladder disposed inside the pliable tube, wherein the bladder has a second unrestrained maximum air capacity that is greater than the first unrestrained maximum air capacity, the bladder being inflated when the deck is raised and deflated when the deck is lowered; and a source of pressurized air coupled to the bladder such that air discharged from the source of pressurized air inflates the bladder, which in turn expands the pliable tube to push the deck upward.
 18. The dock leveler of claim 17, wherein an air gap between the bladder and the pliable tube gets smaller upon inflating the bladder.
 19. The dock leveler of claim 17, wherein the pliable tube is substantially cylindrical when expanded.
 20. The dock leveler of claim 17, wherein the bladder deviates from a cylindrical shape when inflated and unrestrained.
 21. The dock leveler of claim 17, wherein the bladder is generally pillow-shaped when inflated and unrestrained.
 22. The dock leveler of claim 17, wherein the bladder is more airtight than the pliable tube.
 23. The dock leveler of claim 17, wherein the pliable tube is stronger than the bladder.
 24. The dock leveler of claim 17, wherein the bladder comprises two pliable sheets integrally joined to each other by a peripheral joint, whereby the two pliable sheets and the peripheral joint are of the same material.
 25. The dock leveler of claim 17, further comprising a nozzle that couples the source of pressurized air to the bladder, wherein the nozzle defines an air passageway that provides a diverging flow pattern of air discharged from the source of pressurized air.
 26. The dock leveler of claim 25, wherein the air passageway extends along a curved centerline that defines an obtuse angle.
 27. The dock leveler of claim 17, wherein the lip extension is linearly moveable relative to the deck.
 28. The dock leveler of claim 17, wherein the source of pressurized air is at a substantially fixed location.
 29. The dock leveler of claim 17, further comprising a flexible tube that couples the source of pressurized air to the bladder.
 30. A method of operating a dock leveler that includes a deck and a lip extension, wherein the deck is lifted by a bladder disposed inside of a pliable tube, and an air gap exists between the bladder and the pliable tube, the method comprising: inflating the bladder to raise the deck; while raising the deck, exhausting air from within the air gap; moving the lip extension relative to the deck; and deflating the bladder when the deck is lowered.
 31. The method of claim 30, further comprising: in the event of a bladder failure, using the pliable tube to lower the deck at a controlled rate of descent.
 32. The method of claim 30, further comprising pivoting a lip extension relative to the deck.
 33. The method of claim 30, further comprising sliding a lip extension relative to the deck.
 34. A method of using a bladder disposed inside of a pliable tube to raise a deck of a dock leveler that includes a lip extension, comprising: inflating the bladder; while inflating the bladder, exhausting air out from within a gap between the bladder and the pliable tube; expanding the pliable tube by continuing to inflate the bladder; pushing the deck upward by expanding the pliable tube; moving the lip extension relative to the deck; and deflating the bladder when the deck is lowered.
 35. The method of claim 34, further comprising: in the event of a bladder failure, using the pliable tube to lower the deck at a controlled rate of descent.
 36. The method of claim 34, further comprising pivoting a lip extension relative to the deck.
 37. The method of claim 34, further comprising sliding a lip extension relative to the deck. 